There are instances where it is desired to transmit electrical signals between two circuits, while electrically isolating each circuit from the other. This can be accomplished by using photo diodes or other optoelectric transducers to transmit the signal by modulated light. One prior art arrangement involves the use of a circuit board with a pair of electrical connectors for receiving signals and with a pair of optoelectric transducers mounted on the board to face each other, and with each transducer electrically coupled to a different one of the connectors. Such an arrangement is relatively fragile and occupies a considerable area, especially where several separate optical couplings are required and where the apparatus must be shielded from EMI (electromagnetic interference). An optoelectric coupling apparatus which was compact, rugged, and economical, would be useful.